Drill bit condition indicator and signaling system



R. L. ALDER Oct. 16, 1962 DRILL BIT CONDITION INDICATOR AND SIGNALINGSYSTEM Filed July 15, 1955 4 Sheets-Sheet l QOBEET 455 9405? ZZ/I/A R.L. ALDER Oct. 16, 1962 DRILL BIT CONDITION INDICATOR AND SIGNALINGSYSTEM 4 Sheets-Sheet 2 Filed July 15, 1953 R. L. ALDER Oct. 16, 1962 4Sheets-Sheet 3 Filed July 15, 1955 Z5; M 5 w a, #2 mm 1 v pm 5N u 1 G ee lw m. 6 2 4 M W a I 7 J a a. 9 a 0 4 0 9 I H J I w\ M /333 3313 I: mJMc a t- I 4 0 m-\ 6 u 5 p I w L I i--- m n y 7 7. 5 u y M 2 BY Q77?3,058,532 DRILL BIT CONDITION WDICATOR SIGNALING SYSTEM Robert LeeAlder, La Canada, Calif, assignor, by mesne assignments, to DresserIndustries, Inc., Dallas, Tex., a corporation of Delaware Filed July 15,1953, Ser. No. 363,042 4 Claims. (Cl. 175-39) This invention relate ingeneral to improvements in borehole drilling control, and moreparticularly to an improved system for providing signals at the surfaceexterior to the borehole during drilling indicative of certainconditions within the borehole, such as the malfunctioning of the drillbit due to wear.

During drilling operation as conventionally practiced, numerousinstruments have been employed in conjunction with the drillingequipment at the surface exterior to the borehole to provide the drillerwith information regarding the progress of drilling and whether or notproper drilling conditions are being maintained. Such instruments arethe weight indicator, drilling fluid pumping rate and pressure meters,drilling rate meters, rotary table revolution indicators and the like.These instruments, however, have not provided the driller withsufficient information to determine positively whether or not thedrilling tools, such as the drill bit within the borehole, are in propercondition. As a result of this, many failures to maintain properdrilling conditions occur within the depths of the well borehole,particularly at the drill bit.

For example, heretofore, when drilling progress has become slow, thedriller has been unable to determine, during drilling, whether suchslowing down of the drilling rate Was caused by the encountering offormations which are diflicult to drill or whether the bit had becomeworn or damaged to such an extent as to render it unsuited for furtherdrilling. This consequently often resulted either in prematurewithdrawals of the drill string from the borehole for visual inspectionof the drill bit, or the attempt to continue drilling with a drill bitwhich was no longer in proper drilling condition. Either of theseprocedures resulted in waste of time and unnecessary expense.

In some cases, the lack of ability to determine the condition of thedrill bit has resulted in continued drilling efforts after the cuttingcones of the roller bit have frozen to their shaft bearings and thushave stopped rotating. This procedure has resulted in suflicient wear onthe exposed side of the cutting cones to eventually entirely cut awayone side of the cones and a portion of the bearing shaft, permitting therelease of the cutting cones into the well borehole and in some casesthe breakage of the cutting cone shaft itself, resulting in turn inexpensive fishing jobs to recover and remove the cutters and otherbroken pieces of the drill bit from the drill hole.

It is accordingly an object of this invention to eliminate thehereinbefore described difficulties by providing the driller with meansfor obtaining more positive information regarding the condition ofsubsurface drilling equipment while performing drilling operations.

It is a further object of this invention to provide means to determinethe degree of Wear of the drill bit while drilling.

It is another object of this invention to provide a system for giving awarning signal at the surface exterior to the borehole whenever the bitor other subsurface equipment becomes worn to the extent thatreplacement is necessary.

It is a still further object of this invention toprovide an improvedsystem for determining a physical condition within the depths of anearth borehole While carrying on drilling operations and fortransmitting signals indicative of such condition therefrom to theearths surface.

It is still another object of this invention to provide an improvedsystem and means for impressing signal pressure pulsations upon thecirculating drilling fluid stream within the subsurface drilling toolsindicative of existent subsurface conditions.

It is a still further object of this invention to provide improved meansto detect abnormal wear conditions in the drill bit while drilling, andfor the transmission of a fluid pressure signal to the top of theborehole being drilled indicative of occurrence of such abnormal Wearconditions.

The hereinbefore mentioned objects of this invention are in generalaccomplished by providing means for detecting the occurrence orexistence of a predetermined condition within the depths of theborehole, such as, for example, a certain degree of wear on the cuttingsurfaces of the drill bit, and the actuation of drilling fluid flowconstricting means to produce a pressure increase signal in the drillingfluid circulating system when such predetermined condition has beenreached.

Other objects, advantages, and features of novelty will be evidenthereinafter in the more detailed description of the invention.

In the drawings, which illustrate preferred embodiments and modes ofoperation of the invention, and in which like reference charactersdesignate the same or similar parts throughout the several views:

FIGURE 1 is an elevational View, partly schematic and partly inlongitudinal section, illustrating the general arrangement of theapparatus of the invention employed in connection with a typicaldrilling well;

FIGURE 2 is an enlarged longitudinal sectional view, partiallyschematic, of a portion of the apparatus of FIGURE 1 located in thedrill stem adjacent the drill bit, including the drill collar and drillbit;

FIGURE 3 is a transverse sectional view taken on the line 3-3 of FIGURE2;

FIGURES 4, 5, and 6 are fragmentary longitudinal sectional views, inenlarged detail, of alternative constructions of the lower portion ofthe apparatus shown in FIGURE 2;

FIGURE 7 is a schematic wiring diagram of the electromechanical portionof the actuating mechanism employed in connection with the apparatus ofFIGURE 4;

FIGURE 8 is a schematic wiring diagram of an alternativeelectromechanical portion of the actuating mechanism employed inconnnection with the apparatus of FIGURE 4;

FIGURE 8 is a schematic wiring diagram of an alternativeelectromechanical portion of the actuating mechanism employed inconnection with the apparatus of FIGURE 4;

FIGURE 9 is a schematic wiring diagram of the electromechanical portionof the actuating mechanism employed in connection with the apparatus ofFIGURE 5 or FIGURE 6; and

FIGURE 10 is a schematic wiring diagram of the electromechanical portionof the actuating mechanism in connection with the apparatus of FIGURE 1.

Referring first primarily to FIGURE 1, in which the general dispositionof the apparatus of the invention is shown in relation to a conventionaldrilling rig and drilling well, the lower uncased portion of a boreholebeing drilled is shown at 10, and at 11 the upper portion of theborehole is shown in which the usual surface string or conductor stringof casing 12 has been set and cemented.

Within the borehole and at the surface above the borehole is shown asubstantially conventional rotary drilling rig including a drill stringcomprising a drill bit 13, a drill 3 collar 14 and a drill stem composedof drill pipe 15 connected at its upper end through a kelly bar 16 to aswivel 17, which in turn is suspended from a traveling block hook 18,traveling block 19, drilling lines 21), and crown block 21 located inthe top of a derrick 22. The kelly bar 16 passes through conventionalgripping means in a rotary table 25 supported in the usual or suitablemanner upon the derrick floor or foundations. The rotary table isadapted to be rotated by means of the usual bevel gear and pinion rotarytable drive illustrated at 26 and 27, respectively. The pinion 27 iscoupled to be driven in accordance with usual practice through aconventional chain drive or through a suitable shaft drive, asillustrated at 28, by the power unit of a drawworks 30.

The drilling fluid circulation passage, as shown in FIGURE 2, extendingfrom the discharge or wash ducts 23 of the drill bit 13, through thedrill collar 14, and through drill stem 15, kelly bar 16, and swivel 17,is connected at the top through a suitable flexible connection or hose31 and riser and connecting pipes 32 and 33, respectively, to thedischarge connection 35 of a drilling fluid circulating pump 36. Thedrilling fluid circulating pump 36 takes suction through pipe 33 from abody of drilling fluid 3% contained in a mud reservoir or sump 40, as isconventional practice. The upper end of the before-mentioned surfacecasing 12, which provides a return path for circulating drilling fluidrising around the drill stem from the open borehole therebelow, isprovided with a lateral or side outlet pipe 42 which extends to anddischarges into the drilling fluid reservoir 40.

A surge chamber 45 or other suitable surge dampening means is preferablyconnected to the discharge 35 of the drilling fluid circulating pump 36for the purpose of smoothing out or reducing the pump discharge pressurefluctuations.

A suitable pressure pickup device 47 is connected hydraulically to thefluid passage within the discharge pipe 33. The pressure pickup device47 may be of any suitable type, but preferably one such as, for example,the Statham Laboratories Pressure Transducer, Model No. P10, adapted toconvert fluid pressure communicated to it from pipe 33 intocorresponding values of electric current or potential. This transducermay be energized by a suitable electric current supply such as a batteryor other suitable current source illustrated at 48 in FIGURE 1, and whenso energized is capable of producing an electric output signal which isa function of the instantaneous fluid pressure applied to it, whichpressure in the present case is that appearing in pipe 33. The pressurepickup device 47 is connected through insulated conductors 49 to asuitable pressure measuring device 50 which may be a pressure indicatoror preferably a recorder such as, for example, the Minneapolis-HoneywellStrip Chart Potentiometer manufactured by the Minneapolis-HoneywellRegulator Company, and by means of which the pressure variations orchange in pressure throughout the drill stem, as it appears in pipe 33,may be continuously recorded on a chart 46 moving at a constant orsuitable speed.

Referring now primarily to FIGURES 2 and 3, the drill collar 14mentioned hereinbefore in connection with FIGURE 1 comprises asubstantially solid, tubular, lower section 52 of suitable length andweight and a tubular upper section 53 formed with suitable annularchambers or cavities as shown at 54 and 55 for containing the electricaland mechanical apparatus hereinafter more fully described.

The upper end of the drill collar 14 is joined, by a suitable threadedconnection or coupling 51, with the before-mentioned upwardly extendingdrill pipe 15, and the lower end of the drill collar is connected by theusual box and pin type of threaded tool joint or coupling 61 to thebefore-mentioned drill bit 13. The upper portion 53 of the drill collar14 contains an inner, concentric liner member 64 which defines an upperdrilling fluid passage 56, and the lower portion 52 of the drill collaris provided with a central, longitudinally extending, lower drillingfluid passage 57 terminating at its upper end in an upwardly extendingnipple 68. The lower end of the liner 64 constituting the upper fluidpassage 56 and the upper end of nipple 68 of the lower fluid passage 57,as provided within the upper and lower portions of the drill collar asbefore described, terminate coaxially opposite one another as shown at58 and 59, respectively, forming a gap therebetween which isinterconnected by means of a resilient, tubular member 60. The upper andlower ends of the resilient, tubular member 60 make fluid-tightconnection with the lower end 59 of the liner 64 and with the upwardlyextending nipple 68, respectively, and are held in such fluid-tightconnection by hose clamps, as illustrated at 62 and 63, or by othersuitable connecting means. The resilient, tubular member 60 ispreferably composed of rubber, neoprene, or other suitable resilient orrubber-like material, whereby it will be capable of being readilydeformed to restrict the flow of fluid flowing through and between thefluid flow passages 56 and 57, as hereinafter more fully described.

Located within the before-mentioned apparatus chamber is suitablehydraulically actuated means for constricting the hereinbefore-mentionedresilient sleeve member to increase the resistance to flow of fluidtherethrough, as before mentioned. In the illustrated embodiment of thisinvention such means comprises a pair of oppositely positioned,approximately semicircular lever members 65 and 66 which togethersubstantially encircle the midsection of the resilient, tubular member60 intermediate the upper and lower ends thereof, as best shown inFIGURE 3. The lever members 65 and 66 are each hinged for scissor-likepivotal motion toward one another about a common hinge pin 67 whichpasses through one end of each of the aforesaid lever members 65 and 66and through a supporting lug 69 attached to and extending inwardly fromthe inner wall of the chamber 55.

The opposite ends of the levers 65 and 66 are provided with overlappinggusset members 70 and 71 which terminate in laterally extending lugs 72and 73, which are pin-connected as shown at 74 and 75 to a piston and acylinder 76 and 77, respectively, of a hydraulically actuated unit. Theinternal clearance space between the head of the cylinder 77 and thepiston 76 is connected through a suitable pressure tubing 79 to thepressure end of a hydraulic actuating cylinder 80 also located withinthe chamber 55.

The hydraulic actuating cylinder 80 is provided with a piston 81 whichis connected through a piston rod 32 to the lower end of anannular-shaped armature 83 of a solenoid 85 which surrounds anintermediate portion of the liner 64. For this construction the liner 64is composed of a suitable non-magnetic material such as stainless steel,Monel metal or the like. The solenoid 85 is provided with aferro-magnetic shell 84 and core member 86 enclosing annular fieldwindings 87, such that upon energizing the solenoid by passing asuitable electric current through the windings 87 the armature 83 isforcefully urged to move longitudinally upward into the windings andshell by the resultant magnetic forces Within the solenoid.

The apparatus chamber 55 containing the sleeve member 60 and thebefore-described apparatus for constricting it is closed from allcommunication with the exterior of the apparatus except insofar as fluidpressures are transferred to it from the drilling fluid flow ductsthrough the flexible walls of the sleeve member 60, and is filled withliquid, preferably oil. This is an important feature of this embodimentof the invention herein illustrated for several reasons. First, thefilling of the entire space 55 with liquid serves to maintain anecessary degree of equalization of the static fluid pressure on theexterior and interior surfaces of the sleeve member 60 regardless of thepressure exerted by the drilling fluid on the interior thereof as theapparatus is lowered into the fluid in deep well boreholes. Second, inthe absence of communica tion of the liquid filled chamber 55 with thefluid pres sures exterior to the apparatus, except through the sleeve'60 itself as before mentioned, the sleeve member is imparted a supportby such liquid, and at the same time a stability against substantiallycomplete inward collapse once constriction thereof is initiated due tothe dynamic fluid pressure differential set up between the interior andexterior surfaces thereof when drilling fluid is flowing therethrough.Such collapse of the sleeve 60, which otherwise occurs in the absence ofthe foregoing conditions, persists after the initial constricting forcehas been removed, and hence the restriction to flow once initiatedcannot be removed.

However, the foregoing instability is prevented by maintaining thechamber 55 closed and filled with liquid, and under such conditions theconstricting force applied thereto by the beforementioned lever members65 and 66 serves to pinch the sleeve member 60' inward at the point ofcontact of the lever members 65 and 66 therewith and to cause an outwarddeflection of adjacent portions thereof such as to maintain the volumeof liquid in the chamber 55 exterior to the sleeve 60 substantiallyconstant. Under the latter conditions, the constriction of the sleeve 60can be applied and removed at will, and stability will be maintained.

Within the upper apparatus chamber 54 within the drill collar, iscontained an instrument housing 89, which may for convenience ofinstallation be in the shape of an annulus or segment of an annulus andpreferably fluid-tight, which contains the electrical apparatusillustrated herein and hereinafter more fully described in connectionwith FIGURES 7, 8, 9, and 10. The opposite ends of the windings 87 ofthe solenoid 85 are connected through suitable insulated conductors 90and 91 which extend through suitable passages in the bulkhead separatingthe upper apparatus chamber 54 from the lower apparatus chamber 55 andinto the beforementioned instrument case 89 to make connection with theelectrical apparatus therein.

Supported concentrically within an intermediate portion of the flowpassage 57 in the lower portion 52 of the drill collar 14, is a hollowcylindrical housing member 95. A plurality of thin, radial web members,as shown in longitudinal section at 97, serve to support and to retainthe housing 95 centralized in the flow passage 57 with, in eifect, anannular clearance space therearound for passage of fluid. Thebefore-mentioned cylindrical housing 95 is formed with an inner,concentric, cylindrical-shaped chamber 96, out through the lower end ofwhich extends a concentric bore 98 and through the upper end of whichextends an opening 99. The upper opening 99 is covered and sealed overwith a metal bellows 100 which makes fluid-tight connection at its lowerend periphery with the upper end portion of the cylindrical housing 96,thereby placing the inside volume of the bellows in communication,through the opening 99, with the chamber 96. An elongated push rod 102extends into the chamber 96 through the before-mentioned bore 98 withinthe chamber 96 in the housing 95 and is retained therein, with freedomfor limited longitudinal sliding motion therein, by means of an annularstop washer 103 fixed upon a suitable, upwardly facing shoulder formedon and adjacent the upper end of the push rod. A helical spring 104surrounding the upper end portion of the push rod 102 above the stopwasher 103 acts in compression between the upper inside end portion ofthe chamber 96 and the upper face of the stop washer 103 to urge thepush rod 102 downward through the bore 98. A stop lug 105 extendingoutward from the inside surface of the chamber 96 serves, by engagingthe lower side of the stop washer 103, to limit the extent of downwardmotion of the push rod 102. The chamber 96 and bellows 100 are filledwith a liquid, preferably a non-conductive liquid such as oil, toequalize the internal and external pressures thereof when immersed indrilling fluid within a well borehole.

Longitudinally slidably retained upon push rod 102 above a lower stopwasher member 107 is a tapered plug 108 having a downwardly convergingfrusto-conical exterior surface as shown at 109, making a substantiallyfluid-tight fit in a correspondingly shaped plug seat in a centralopening formed in the bottom of the central fluid passage in the shankof the drill bit 13'. A helical spring 110 acting under compressionbetween the lower exterior end portion of the housing and the upperannular surface of the tapered plug 108 serves to urge the plug 108downward into seated position upon the before-mentioned correspondinglytapered seat in the drill bit 13 when the drill bit 13 is assembled tothe drill collar as shown in FIG- URE 2. Suitable O-ring seals areprovided for maintaining a fluid-tight seal between the exterior of theplug 108 and its seat, between the push rod 102 and the tapered plug103, and between the push rod 102 and the housing 95.

The minimum diameter of the lower end opening 111 of the tapered seat inthe drill bit 13 is sufiicient to permit the disconnection of the bit 13from the drill collar 14 at threaded joint 61 and the withdrawal of thedrill bit 13 over the lower stop washer member 107 and the lower endrunner mechanism of the rod 102, hereinafter more fully described.

The lower end of the push rod 102 is curved slightly at an angle such asto direct the end thereof substantially perpendicularly toward the uppersurface of rotation of the cutter teeth of the roller 115.

Attached to the lower end of the curved portion of the push rod 102 is arunner member 112 of sufiicient length to extend circumferentiallybetween and bridge the gap between two or more adjacent teeth of roller115 of the drill bit 13. Normally, when the drill bit 13, in an unworncondition, is assembled to the lower end of the drill collar 14, asshown in FIGURE 2, the runner 112 bears lightly upon the tips of thecutter teeth of the roller, thereby holding the push rod 102 against thedownward thrust of spring 104 in an upward position, substantially asshown in FIGURE 2. As wear of the teeth of the roller 115 progresses,the runner 112 bearing upon and following the shortening of the teeth,permits the push rod 102 to move progressively downward through the bore98 relative to the housing 95 and thus to move the stop washer member103 downward to a position, ultimately, in contact with the stop lug 105under conditions of maximum bit wear.

Within the chamber 96 of the housing 95 and electri cally insulatedtherefrom is positioned an electric contactor 116 which is connectedthrough an insulated electric conductor 117 to the electrical apparatuswithin the instrument housing 89. The insulated conductor 117 passesthrough suitable passages within the lower chamber 55 and thence throughsuitable passages as shown at 118 to the before-mentioned entrance intothe instrument housing 89 located in the upper cavity 54.

As the push rod 102 moves downward following the progressive wear of thedrill bit roller 115, the stop washer member 103 is finally brought intoelectrical contact with the contactor 116, whereby electrical connectionis completed between the conductor 117, contact point 116, and the rod102, which makes an electrical ground return connection through thehousing 95 and other metal portions of the drill collar and bit.

The chamber 96 and the bellows are filled with oil or the likenon-conductive liquid. The chambers 54 and 55 surrounding the instrumenthousing 89 and. surrounding the resilient sleeve 60 are also filled withoil or the like liquid to equalize the internal fluid pressures in thechambers and on the exterior of the resilient sleeve 60 with that of thecirculating fluid in the liner 64 and passage 57.

Referring now primarily to FIGURE 4, a modified form of the wearindicating apparatus is shown in the lower end of the drill collar. Inthis version of the apparatus, a tubular member 121 extends coaxiallydownward from and is supported at its upper end centrally within thelower portion of the fluid passage 57 by means of a pair or a pluralityof radially extending web members 121 around which a clearance space isprovided for passage of the circulating drilling fluid. Longitudinallyslidably carried on the lower end portion of the tubular member 120 is atapered plug 122 which is similar in form to plug 108 hereinbeforedescribed in connection with the apparatus of FIGURE 2. The tapered plug122 is urged downward into seating engagement within thebefore-described tapered seat 109 within the bottom of the fluid passageof the shank of the drill bit 13 by means of the helical spring 125acting in compression between the upper surface of the plug 122 and thelower edges of the web members 121. Extending downward from the tubularmember 121 is a ferro-magnetic projection or pole piece 126 of reduceddiameter, curved adjacent its lower end in a manner similar to that ofthe push rod 102 hereinbefore described in connection with FIGURE 2, andwhich serves as a magnetic core for the windings of a surroundinginductor coil 127 fixed thereon. The inductor coil 127 comprises aplurality of turns of relatively small, insulated wire wound around theupper portion of the pole piece 126 and covered by a non-magnetic,fluid-tight case 128.

As before mentioned, the lower end of the pole piece 126 is curved orbent laterally at an angle such as to position the lower end thereofclosely adjacent the tips of the cuttmg teeth of the roller 115.Sufiicient clearance, however, 15 provided between the tips of thecutter teeth of a new, unworn roller or cone and the end of the polepiece 126 to just avoid contact therebetween. Attached to and forming aportion of the lower end of the pole piece 126 is a permanentlymagnetized member 129', the axis of the magnetic pole thereof beingsubstantially coaxial with the axis of the lower end portion of the polepiece 126, whereby the magnetic flux induced by such permanent magnetwill normally flow from the lower end of the permanent magnet through asubstantially closed magnetic circuit comprising the cutter teeth of theroller or cone 115, through the body of the cone 115, through the coneshaft supporting legs of the drill bit 13, and return through thetransverse lower portion of the drill bit 13, tapered plug 122, and thebefore-mentioned pole piece member 126.

One end of the winding (not shown) of the inductor coil 127 is suitablygrounded to the case 128 or member 125, whereby it makes a ground returnconnection through the body of the drill bit. The other end of thewinding of the coil 127 is connected to an insulated conductor whichleads up through the passageway in the tubular supporting member 120, asshown at 139, and thence through a lateral passageway through web member121, and makes connection with the insulated conductor 117 which leadsto the electrical apparatus in the instrument housing 89, as describedhereinbefore in connection with FIGURE 2.

Referring now primarily to FIGURE 5, in which still another modificationof the apparatus of this invention is illustrated, a tubular supportingmember 135 is supported coaxially within the lower portion of the fluidpastsage 57 in the drill collar by means of a transverse web member orradial web members 136 similar to that shown at 121 in FIGURE 4. Thelower end of the tubular member 135 is provided with an enlarged,hollow, spherical end portion 138 which constitutes a gamma raydetector, as hereinafter described. Longitudinally slidably retainedupon the tubular member 135 is a tapered plug member 140 similar in formto plug 108 or 122 as hereinbefore described in connection with FIGURES2 and 4, and this plug is urged into fluid-tight seating position withinthe correspondingly shaped seat in the drill bit shank, by means of thehelical spring 14-2 also acting in a manner similar to that hereinbeforedescribed in connection with the spring of FIGURE 4. An electrodelocated within the enclosure 138, and which enters the enclosure througha gas-tight insulating seal 144, is connected electrically through aninsulated conductor 143 which extends through the passage in the tubularmember 135 and thence through lateral passage 131 in the transverse webmember 136 into electrical connection with the insulated conductor 117,which in turn extends to the electrical apparatus in the instrumentchamber 89, as hereinbefore described.

The before-mentioned enlarged spherical portion 138 at the lower end ofthe tubular member 135 is made of a suitable metal and constitutes agamma ray detector which may be either of the ionization chamber orGeiger counter type, and is filled with a suitable gas under suitablepressure as is well known in the art.

A plurality of the teeth of either or both of the cutter cones 115 and115a of the bit 13 are made to contain radioactive material capable ofradiating gamma rays, such as, for example, radium, and any one of anumber of suitable radioisotopes such as, for example, cobalt 60 orcadmium 115. Such radioactive material is preferably mixed into themetal melt from which the cutter teeth are formed or included in thehard facing metal which is applied to the tips of the cutter teeth bythe gas or electric welding methods commonly employed for such hardfacing application. The ionization chamber or Geiger counter 138 is, asbefore described, positioned adjacent the cutter teeth of the cuttercones 115, whereby radiation from the radioactive material in the cutterteeth will activate the chamber 138 to a predetermined degree prior tothe occurrence of any wearing away of the cutting teeth during drillingoperations.

The radiation detector 138 is of such size, as shown, as to permit thedrill bit 13 to be detached from the tool joint or lower end of thedrill collar, allowing the plug to be withdrawn from its seat andpermitting the radiation detector 138 to remain suspended on the tubingmember 135 at the lower end portion of the fluid duct 57. Removal andreplacement of the drill bit 13 may thus be readily accomplished withoutthe necessity of assembling or disassembling any of the apparatus,including the ionization chamber or Geiger counter 138 and supportingtubing 135, contained within the lower end of the drill collar.

Referring now primarily to FIGURE 6, in which a modified version of theapparatus of FIGURE 5 is illustrated, instead of the radiation detector138 alone being suspended on the lower end of the tubular member 135, ametal container body, as shown at is suspended at the lower end of thetubing member 135. The container member 150 contains within a suitablerecess on one side thereof, as illustrated at 151, a quantity ofradioactive material capable of producing gamma rays. On the oppositeside of the container 151) and contained within a suitable recesstherein, as illustrated at 152, is a suitable detector of gamma rays,such as preferably an ionization chamber or Geiger counter. The gammaray source 150 and the detector 152 are thus separated as shown at 153by a relatively thick body of shielding material preferably composed ofsteel or lead, whereby the ionization chamber or Geiger counter 152 issubstantially shielded from the direct radiation from the gamma raysource 151.

The electrode (not shown) within the radiation detector 152' isconnected through an insulated conductor 155 to the insulated conductor117 which leads to the instrument housing 89 in the same manner ashereinbefore described in connection with FIGURES 2, 4, and 5.

Referring now primarily to FIGURE 10, in which the electromechanicalportion of the actuating mechanism employed in connection with theapparatus of FIGURE 1 is schematically and diagrammatically shown,conductor 117, which leads from the contactor 116, as described inconnection with the apparatus of FIGURE 2, passes into the instrumenthousing 89 shown in FIGURE 2 and indicated by the dotted line enclosure89 in FIGURE 10, and makes connection with one terminal of a suitablesource of electric current such as one terminal of a battery B. Theother terminal of battery B makes connection through conductor 91 to oneend of the field winding 87 of the solenoid 85. The other end of thewinding 87 is connected through conductor 90 to a suitable groundconnection G within the housing 89. An electric circuit is thus formedfrom one terminal of the battery B through conductor 117 to the contactpoint 116, and when the circuit is completed between the contactor 116and the contactor washer 103, as hereinafter more fully described, thecircuit extends through the ground circuit through the metallic portionsof the drill collar to the ground connection G, and from there in returnthrough conductor 91?, the winding 87 of the solenoid 85, and conductor91 to the other terminal of the battery B.

Referring next to FIGURE 7, in which is illustrated theelectromechanical apparatus employed in connection With the apparatus ofFIGURE 4, the insulated conductor 117 leading from the inductor coil 127passes into the housing 89 and makes connection with one inputconnection of an alternating current amplifier 1613. The other inputterminal of the amplifier 160 makes connection through the ground G andthe metallic portions of the drill collar and bit to the grounded end ofthe inductor coil 127. The output from the alternating current amplifier160 is connected through conductor 161, rectifier 162, conductor 163, tothe windings of an electromagnet 165 of a relay 167 and return throughconductor 166. An electric capacitor C is connected between conductors163 and 166, across the windings of the electromagnet 165. The capacityof the capacitor C and the resistance of the windings of theelectromagnet 165 are made such as to provide an electric time constantin the circuit comprising the capacitor C and the windings of theelectromagnet 165 which is relatively long as compared to the frequencyof the alternating current input to the amplifier 160, which isgenerated by the roller bit cutter teeth and the inductor coil 127acting as a generator, as hereinafter more fully described.

The relay armature 168 is urged normally into electrical contact witthcontact point 16? by means of spring 170 when the electromagnet 165 isnot energized. The armature 168 is connected through conductor 172 toone terminal of a suitable source of electrical current such as batteryB. The other terminal of the source of electric current B is connectedthrough conductor 91 to one end of the windings 87 of the solenoid 85.The other end of the windings 87 is connected through conductor 90 tothe before-mentioned relay contact 169.

Referring now to FIGURE 8, in which an alternative version of theelectromechanical portion of the actuating mechanisms which may beemployed in connection with FIGURE 4 is illustrated, conductor 117leading from the inductor coil 127 enters the instrument housing 89 andmakes connection with one input terminal of an oscillation generator175. The other input terminal of the oscillation generator 175 makesconnection through the ground connection G and through the body of thedrill collar and bit to the grounded end of the inductor coil 127 in themanner hereinbefore mentioned. The oscillation generator 175 may be ofany suitable type, the frequency of which is capable of being controlledin accordance with the variations in reluctance of the magnetic path ofthe apparatus constituting, in effect, the magnetic core of the inductorcoil 127. For example, in the present embodiment, the coil 127constitutes an inductance in the oscillatory circuit of an electron tubeoscillator of conventional design, whereby variation of the inductanceof the inductor coil 127 will cause a corresponding variation infrequency of the oscillator. Considerable latitude in oscillatorfrequencies which may be employed is possible, a frequency of 1000cycles per second being suitable.

The alternating current output of such oscillator is fed through thepair of conductors 177, 178 to the input of a frequency discriminatingcircuit schematically illustrated at 181. Such frequency discriminatingcircuit 181 may be of any suitable or conventional type capable ofproducing preferably a D.-C. or unidirectional output signal or currenthaving a value which is a function of the input frequency appliedthereto through conductors 177 and 178, and in the present case suchD.-C. or unidirectional output from the discriminator is applied throughconductors 182 and 183 to the windings of the electromagnet 185 of relay186.

Armature 195 of relay 186 is urged into its closed position with respectto contact point 197 by means of a spring 198. The armature 195 of relay186 is connected through conductor 214 to one terminal of battery B andthence from the other terminal of battery B through conductor 91 to oneterminal of the windings 87 of the solenoid 85. The contact point 197 ofthe relay 186 is connected through conductor 20 to the other end of thewindings 87 of the solenoid in the manner shown more completely inFIGURE 7.

Referring now to FIGURE 9, in which the electric circuit employed inconnection with the apparatus of FIG- URES 5 and 6 is illustrated, theconductor 117 leading from either the ionization chamber or Geigercounter 138 of FIGURE 5, or from the ionization chamber or Geigercounter 152 of FIGURE 6, enters the instrument housing 89 and makesconnection with one input terminal of an electrometer or pulse counter216 of suitable type. The other input terminal of the electrometer orpulse counter 216 makes a return connection with the grounded terminalof the ionization chamber or Geiger counter through ground connection G.

The electrometer or pulse counter 216 may be of any suitable orconventional type, which includes a suitable potential source forapplying a relatively high potential diiference between, for example,the electrode 139 and the surrounding envelope of the ionization chamber138. The electrometer or pulse counter also may include conventionalapparatus for producing preferably an A.-C. or pulsating D.-C. outputsignal in conductors 217 and 218 which is proportional to or a functionof the ionization current or pulses in the before-mentioned radiationdetectors 138 or 152.

The resultant A.-C. or pulsating D.-C. output signal from theelectrometer or pulse counter 216 is applied through conductors 217 and218 to the input terminals of an A.-C. amplifier 220, and from theamplifier 220 the A.-C. output signal from the amplifier is passedthrough conductors 221 and 222 and rectifier 229 and the resultant DC.signal to the windings of electromagnet 223 of the relay 224. Thearmature 225 of relay 224 is normally urged into a closed position withrespect to contact point 226 by means of spring 227. The relay armature225 is connected through conductor 228 to one terminal of a suitablesource of electric current such as battery B. The other terminal of thesource of electric current B is connected through conductor 91 to oneterminal of the windings 87 of the solenoid 85, and the other terminalof the windings 87 of the solenoid 85 makes return connection throughconductor to the contact point 226 of the relay 224, as hereinbeforedescribed more fully in connection with FIGURE 7.

The operation of the apparatus of the invention is as follows:

Referring first primarily to FIGURE 1, the drilling fluid, which isusually in the form of an aqueous drilling mud as commonly employed inthe drilling industry, is continuously withdrawn from the reservoir orsump 40 through the suction pipe 38 of the drilling fluid circulatingpump 36 and discharged under pressure from pump 36 through pipes 33 and32, through the flexible hose 31, and thence through the swivel 17 intothe fluid passage in the kelly bar 16. The drilling fluid continues inits flow downward through the kelly bar 16, through the sections of thedrill pipe 15 comprising the drill stem and through .the passages 64 and57 in the drill collar to the drill bit 13, from which it is dischargedthrough the drill bit fluid outlet passages 23 into the bottom of theborehole surrounding the drill bit. From the bottom of the borehole thedrilling fluid, together with cuttings from the drill bit, flows upwardthrough the annular space in the borehole surrounding the drill stem andup through the surface string of casing 12, from which it overflowsthrough the lateral or side outlet pipe 42 and returns to the sump 40.

The surge chamber 45 acts partially to absorb and smooth out thedrilling fluid flow pressure fluctuations from the pump 36 resulting inflow of the drilling fluid from the pump to and through the drill sternhaving pressure pulsations and fluctuations which are of relatively lowamplitude. Meanwhile, the rotation of the drill stem and drill bit bymeans of the rotary table may or may not be simultaneously maintained,as the occasion dictates.

Referring now first primarily to the operation of the apparatus ofFIGURES 1, 2, and 3, as the drill stem, drill collar, and drill bit 13*are rotated on bottom during drilling operations, the cutting tips ofthe cutter teeth on the rollers or cones 115 are subject to progressivewear, which gradually shortens them and causes a corresponding decreasein the eifective diameter of their circle of revolution. As the diameterof the circle of revolution of the teeth of the cones 115 thus reduces,the runner 112, which rides lightly upon the ends of the cutter teeth,under the downward pressure exerted by spring 110, permits the rod 102to move downward correspondingly gradually. When the diameter of thecircle of revolution of the tips of the cutter teeth of the rollers 115has thus reached a predetermined minimum, as determined by the initialadjustment of the position of the contactor point 116 in the chamber 96,the contact washer 103 will have then moved downward into electricalcontact with the aforesaid contactor 116. At this point, electricalconnection of the contactor 116 is made to ground through the rod 102and return through the metallic portions of the drill collar, therebycompleting the electrical circuit between the ground G and the conductor117 shown in the wiring diagram of FIGURE 10. Current is thus permittedto flow from the current source B through conductor 91 to the windings37 of the solenoid 85 and return through conductor 9i) and ground G toconductor 117. The solenoid 85, thus energized, applies an upward forcefrom the solenoid armature 83 through the piston rod 82 to the piston 81in cylinder 80. The resultant upward motion of the piston 8-1 appliespressure to the liquid contained in the upper end of the cylinder 80,which pressure is transmitted through the tubing 79 to the inlet of thehydraulic cylinder 77. The resultant equal and opposite forces appliedto the cylinder 77 and the piston 76 therein, as applied to the pinconnections 75 and 74, respectively, cause the lug 72 to move upward andthe lug 73 to move downward, as viewed in FIGURE 3 of the drawings,thereby causing the lever members 65 and 66, respectively, to pivotabout pin 67 in scissor-like movement toward one another. Such pivotalmotion of the lever members 65 and 66 toward one another brings theminto contact with the exterior surface of the resilient sleeve member60, thereby deforming the sleeve member 64 by depressing or pinching itinward in such a way as to reduce the cross-sectional area of the fluidflow passage therethrough, as illustrated by dotted lines 61.Constriction of the sleeve member 6% to produce a fluid pressure risethereabove of from approximately 50 to 100- psi. is usually sufficient.

The resultant increased pressure drop through the sleeve 64) causes acorresponding pressure increase thereabove throughout the fluid passagein the drill stem, and this fluid pressure increase is communicatedthrough the swivel 17, the flexible hose connection 31, and riser andconnecting pipes 32 and 33 to the discharge of the fluid circulatingpump 36. The pressure rise thus communicated to the pipe 33 is detectedby the pressure pickup device 47 and converted into a correspondingelectrical signal which may be utilized to operate any desired type ofaudible or visible signaling device. In the embodiment hereinillustrated, this signal is recorded on the moving chart 46 of recorder50 as a line appearing substantially as illustrated at P in FIGURE 1.The 00- currence of such a pressure change as is illustrated by theoffset line at P on the chart 46 then indicates to the driller that thewear on the rollers of the bit has progressed to the predetermined pointat which replacement of the bit with a new hit should be made. The drillstem may then be withdrawn from the borehole, and the worn drill bitreplaced by a new drill bit, as required.

Reference is now made primarily to the operation of the apparatus ofFIGURES 4 and 7. Rotation of the drill bit on bottom during drillingoperations causes the rollers to rotate relative to the stationaryelectromagnet 128 carried on the lower end of the pole piece 126. As thecutter teeth on the rollers 115 are thus caused to move past the lowerend of the magnet 128, the periodic variation in the gap or spacingtherebetween causes a correspondingly periodic variation in thereluctance of the magnetic flux path through the circuit consisting ofthe pole piece 126, the permanent magnet 129, the cone 115, thecone-supporting legs and shank of the drill bit, and return through theplug 122 and the lower end portion of the tubular member 120. Suchperiodic variation in the reluctance of the magnetic flux path causes acorresponding Variation in the flux passing through the inductor coil127, which in turn results in inducing an alternating electric potentialin the windings thereof, which is applied through the conductor 117 tothe input of the alternating current amplifier and return through theground connection G and through the body of the drill collar and bit.The resultant alternating current output from the amplifier 160 isrectified at 162, and the resulting unidirectional current flows throughconductor 163 to the windings of the electromagnet 165 of the relay 167,and return through conductor 166. The capacitor C is charged at apotential equal to the potential drop across the windings of theelectromagnet 165. As hereinbefore mentioned, the time constant of theelectrical circuit consisting of the capacitor C and the windings of theelectromagnet 165 is relatively long as compared to the frequency of thealternatirig current normally applied to the amplifier 160 and thusrelatively long as compared to the resultant pulsations in theunidirectional current resulting from the rectification of the outputfrom the amplifier 160 by the rectifier 162. The relay 167 will thus notbe actuated by any of the individual pulsations of the pulsatingunidirectional current applied to it.

As the cutter teeth of the roller 115 progressively Wear shorter andshorter during drilling operations, the gap separating the lower end ofthe magnet 129 from the tips of such cutter teeth will graduallyincrease, and at the same time the resultant blunting of the cutterteeth by such wear will result in a decreased range and rate ofvariation of the reluctance of the before-mentioned magnetic flux pathas the cutter teeth are rotated past the lower end of the magnet 129.All of these eifects result in a corresponding decrease in amplitude ofthe alternatin voltage or current induced in the inductor coil 127, fora given rate of drill bit rotation and corresponding rate of cutterroller or cone rotation, which in turn results in a correspondinglydecreased rectified unidirectional potential output from the amplifier160 and rectifier 162 being applied across the capacitor C and acrossthe windings of the electromagnet 165 of the relay 167. By adjustment ofthe tension of spring 170, the armature 168 of relay 167 is made to moveinto contact with contactor point 169 at a predetermined minimum currentthrough the electromagnet 165. Thus, when such a predetermined minimumcurrent through the electromagnet 165 has been reached, as thealternating signal input to the amplifier 160 decreases due to wear ofthe cutter teeth on the roller 115, as before described, the armature168 of relay 167 moves into contact with contactor point 1169, therebycompleting the electrical circuit from the battery B through thewindings 87 of the solenoid 85. The current thus applied to the windings87 of the solenoid 85 causes the solenoid armature 83 to move upward,thereby moving the piston rod 82 and the piston 81 in the cylinder 80upwardly, thereby in turn applying pressure through the tubing 79 to thehydraulic cylinder 77 of the valve mechanism in the same manner and withthe same results as hereinbefore described in connection with FIGURES 2and 3.

Since the amplitude of the signal induced in the inductor coil 127 willnot only vary as the wear of the cutter teeth varies, but also will varyas the speed of rotation of the cutter cone varies, it will be necessaryto standardize on the speed of rotation of the drill bit at which it isde sired to determine Whether or not the drill bit has reached thedegree to which the apparatus is adjusted to actuate the signalingmeans, as before described.

If, for any reason, such as damage or wear to the roller bit, the cone115 ceases to rotate, the alternating potential ordinarily induced inthe inductor coil 127 will likewise cease, resulting in actuation of theelectrical circuit as before described and the constriction of theresilient sleeve 60, in turn causing a pressure rise to occur throughoutthe drill stem which is detected and recorded by the recorder as shownat P.

Reference is now made primarily to the operation of the apparatus ofFIGURES 4 and 8. In the operation of this apparatus, the inductor coil127 is connected through conductor 117 and the ground return connectionto the input connections of an oscillation generator 175, ashereinbefore described. Rotation of the roller 115 relative to the polepiece 126 and the resultant variation in the reluctance of the magneticflux path through the inductor coil 127 result in a correspondingperiodic change in the inductance of coil 127. Since the inductance ofcoil 127 constitutes a controlling factor in the oscillatory circuit ofthe oscillation generator 175, as before described, the frequency ofoscillation thereof is thereby modulated at a frequency corresponding tothe frequency of passage of the cutter teeth past the lower end of thepole piece 126 and at a frequency modulation range which is a functionof the shape of the cutter teeth, the maximum range occuring with sharp,unworn teeth and decreasing with wear and blunting thereof. In thisarrangement, the lower end portion 129 of the pole piece 126 need not bea permanent magnet, but may be merely a piece of ferromagnetic materialsuch as soft iron or steel. The thus modulated alternating currentoutput from the oscillation generator 175 is applied through conductors177 and 178 to the input of the frequency discriminator 181, whichproduces an output signal therefrom which is a function substantiallyonly of the range of variation of frequency of the alternating currentinput and which is substantially independent of the modulation frequencyover a wide range of frequencies above very low frequencies.

When the cutter teeth are sharp and of maximum angularity of form, therotation of the rollers during drilling produces the maximum range ofvariation of inductance of coil 127, thereby producing the maximum rangeof frequency of modulation of the oscillator 175. As the cutter teethbecome blunted in form due to wear during drilling, they produce acorrespondingly reduced range of variation of inductance of coil 127,whereby the frequency range of modulation correspondingly becomespogressively lower until, if such wear were allowed to continueindefinitely, the ultimate result would be the entire removal of theteeth with resultant zero range of modulation of the oscillator. Theresultant signal output from the discriminator 181 thereforecorespondingly varies from a maximum value when the cutter teeth are newand sharp to a minimum value when the cutter teeth are worn and blunt,with a theoretical ultimate lower limit of zero signal when the teethare entirely worn away.

The condition of maximum allowable wear lies somewhere between these twoextreme conditions, and by suitable adjustment of the relay 186, as, forexample, by adjustment of the tension of spring 198, the relay is set toopen or close when the signal fed to it through conductors 182 and 183from the discriminator 181 is greater or less, respectively, than apredetermined arbitrary value corresponding to a predetermined cutterteeth wear condition.

Thus, so long as the signal fed to the relay 186 has a value above thepredetermined value, the relay will remain open. When, due to cutterteeth wear as before described, the signal fed to the relay 186 from thediscriminator falls below the predetermined value, the relay will close,that is, the armature 195 will move into contact with contact point 197,and the electrical circuit will thereby be completed from one terminalof battery B through conductor 91 to the windings 87 of the solenoid andreturn through conductor 90, contactor point 197, armature 195, andconductor 214 to the opposite terminal of battery B.

If for any reason, such as damage, breakage, or freezing of thebearings, the cutter roller ceases to rotate, variation of theinductance of the coil 127 will correspondingly entirely cease, in turnresulting in lack of any modulation of the output of the oscillationgenerator 175. Such resultant unmodulated alternating current appliedfrom the oscillation generator to the input of the discriminator circuit181 will result in the absence of any output signal from the output ofthe frequency dis criminator. The electromagnet 185 of the relay 186will thus be deenergized, permitting the armature 185 to move intocontact with the contactor point 197, thus closing the electricalcircuit between conductors 214 and 197 and thereby in turn energizingthe solenoid 85 as before described.

Therefore, so long as the roller 115 continues to rotate properly and solong as the wear of the cutter teeth does not exceed a predeterminedamount, relay 186 will be sufficiently energized to maintain thecontacts thereof open, and the solenoid 85 will remain unenergized. If,however, as before mentioned, due to damage or breakage, the roller 115ceases to rotate, then the oscillation generator 175 will cease to bemodulated, and an unmodulated alternating signal will be communicatedfrom the output thereof through conductors 1'78 and 188 to the input ofthe frequency discriminator circuit 181. Since under such condition theinput to the frequency discriminator circuit 181 is unmodulated, therewill be no output signal therefrom through the conductors 182 and 183,and the relay 186, thus being deenergized, will permit the contactbetween armature and contactor point 197 to close, thereby energizingthe windings 87 of the solenoid 85 and in turn thereby actuating thehydraulic system to cause the resilient sleeve 60 to be deformedsufiiciently to cause a pressure rise in the fluid flow therethrough.

In event either one or both of the before-described conditions occurs,that is, if the roller 115 either ceases to rotate or if it incursexcessive wear, a pressure pulse will thus be transmitted and receivedat the top of the well and Will be indicated or recorded as shown at Pon the chart 46 of recorder 50.

Reference is now made primarily to the operation of the apparatus ofFIGURES 5, 6, and 9. Interception of gamma rays by the radiationdetector chamber 138 from the radioactive material placed in the cuttingedges of the cutting teeth of the rollers 115 and 115a, or theinterception of gamma rays by the radiation detector 152 resulting fromthe scattering of gamma rays radiated from the source 151, suchscattering being caused by the presence of the adjacent cutter teeth ofthe rollers 115 and 115a, results in a current flow through conductor143 in the apparatus of FIGURE or through conductor 155 in the case ofthe apparatus of FIGURE 6 and thence through conductor 117 to the inputof the electrometer or pulse counter 216 as shown in FIGURE 9. Theoutput from the electrometer or pulse counter 216 is applied throughconductors 217 and 218 to the input of amplifier 220, and the output inturn of the amplifier 220 is applied through conductors 221 and 222 tothe electromagnet 223 of the relay 224 Normally, prior to the occurrenceof substantial wearing away of the radioactivity-containing tips of thecutter teeth on the cones 115 and 115a, or due to the reduction inscattering of gamma rays, also due to such wearing away of the metal ofthe cutter teeth, the gamma rays intercepted by either of the radiationdetectors 138 or 152 will be suflicient to result in maintaining therelay 224 open, thus maintaining the solenoid 85 deenergized, in turnresulting in the absence of any fluid pressure signal being transmitted.However, upon a predetermined degree of Wearing away of the cutter teethon the cones 115 and 115a, sufiicient radioactive material is removedand carried away or sufficient metal which causes scattering of thegamma rays is also removed and carried aWay to reduce the ionizationchamber current or Geiger counter pulse rate below a predeterminedvalue. The current thus applied from either of the radiation detectors,as the case may be, through the conductor 117 to the electrometer orpulse counter 216 is thus reduced to a value below that resulting in theminimum current required in the windings of the electromagnet 223 tomaintain the contacts of the relay 224 open, thereby permitting thearmature 225 of the relay 224 to move into closed contact with thecontactor point 226. The electrical circult is thereby completed fromthe battery B through the conductors 9t) and 91 to the windings 87 ofthe solenoid 85, causing movement of the piston 81 in the cylinder 80,thereby in turn applying pressure to the hydraulic cylinder 77. Suchpressure applied to the hydraulic cylinder 77 causes the constriction ofthe resilient sleeve 60 resulting in a fluid pressure signal beingtransmitted to the instruments at the surface of the drilling well, ashereinbefore described.

Much of the apparatus has been herein described as located within thedrill collar. However, the term drill collar as herein used is notnecessarily to be limited to the exact construction or locationconventionally employed for drill collars, but shall mean any suitablecontainer forming a part of the drill stem, drill collar, or drill bit,but usually located in the lower part of the drill stem adjacent orclose to the drill bit.

It is to be understood that the foregoing is illustrative only, and thatthe invention is not to be limited thereby, but includes allmodifications thereof within the scope of the invention as defined inthe appended claims.

What is claimed is:

1. In a rotary drill string having a fluid flow duct therethrough and arotatable cutting member journaled thereon for rotational cuttingcontact with formations being drilled, said cutting member having acutter surface subject to wear by said cutting contact, the combinationcomprising: sensing means carried by said drill string and positionedadjacent the said cutting surface, said means being responsive tochanges, due to wear, in location of said cutting surface relative tosaid drill string; signal means in said drill string adjacent saidcutting member,

actuatable to efiect a change in resistance to flow of fluid flowingthrough said duct at a location adjacent said cutting member; and meanscontrolled by said sensing means to actuate said signal means when saidcutting surface has incurred a predetermined change in locationcorrespond ing to a predetermined amount of wear, wherein said sensingmeans comprises: a movable runner member; and means urging said runnermember into engagement slidably with said cutting surface whereby theposition of said runner member relative to said drill string changes asthe location of said cutting surface changes due to wear.

2. Apparatus according to claim 1, in which said means to actuate saidsignal means comprises electromagnetic means operatively coupled to saidsignal means, and in which said means controlled by said sensing meanscomprises an electric current source, and switching means forcontrolling the connection of said current source to saidelectromagnetic means, said switching means being actuated by saidmovable runner member when said runner member has incurred apredetermined change in location.

3. Apparatus according to claim 2, in which said signal means comprisesmovable means in said flow duct movable by said electromagnetic means topartially restrict flow of fluid through said duct.

4. In a rotary drill apparatus, the combination comprising: a drillcollar; a drill bit detachably coupled coaxially to the lower end ofsaid drill collar, said drill bit and said drill collar being providedwith interconnecting, axial, fluid flow passages through said drillcollar and said drill bit; a rotatable cutting member journaled on saiddrill bit for rotational cutting contact with formations being drilled,said drill bit being provided with an axial opening in said drill bitinterconnecting the axial fluid flow passage thereof with the exteriorunderside of said drill bit adjacent said cutting member; a supportingmember attached adjacent one end of said drill collar fluid flow passageto the inner walls of said drill collar fluid flow passage and extendingaxially therefrom through said opening in said drill bit to a positionat which the other end thereof is adjacent said cutting member; sensingmeans carried adjacent the said other end of said supporting member;signal producing means attached to said sensing means by said supportingmember, said signal producing means being adapted to produce a signalindicative of a change in the degree of wear of said cutting member dueto cutting contact with formations being drilled; and closing meanscarried on an intermediate portion of said supporting means todetachably close said opening whereby, upon disconnection of said drillbit from said drill collar, said closing means is Withdrawn from saidopening and said supporting member and said sensing means thereon may bewithdrawn from said drill bit through said opening and retained on saiddrill collar.

References Cited in the file of this patent UNITED STATES PATENTS Re.22,531 Hare Aug. 22, 1944 2,352,833 Hassler July 4, 1944 2,388,141Harrington Oct. 30, 1945 2,434,835 Colley Jan. 20, 1948 2,562,833 TrueJuly 31, 1951 2,575,173 Johnson Nov. 13, 1951 2,590,215 Sausa Mar. 25,1952 2,627,392 Morris Feb. 3, 1953 2,658,724 Arps Nov. 10, 19532,669,871 Lubinski Feb. 23, 1954 CERTIFICATE OF CORRECTION Patent No, 3O58 532 October 16, 1962 Robert Lee Alder Column 2, line 60 after"mechanism" insert employed column 9 line 45, for "witth" read witcolumn 13, line 12, for "upwardly" read upward line 20, for "cone" readconesv line 22, after "bit" insert wear column 14, line 2, for"corespondingly" read correspondingly ERNEST w. SWIDER DAVID LADDAttesting Officer Commissioner of Patents CERTIFICATE OF CORRECTIONPatent No, 3,058532 October 16, 1962 Robert Lee Alder It is herebycertified that error appears in the above numbered patent requiringcorrection and that the said Letters Patent should read as correctedbelow.

Column 2, line 6O after "mechanism" insert employed column 9 line 45,for "witth" read with column 13, llne 12 for "upwardly" read upward line20, for "cone" read cones line 22, after "bit" insert wear column 14,line 2, for "corespondingly" read correspondingly ERNEST w. SWIDER DAVIDLADD Attesting Officer Commissioner of Patents

